Having survived extreme weather, appalling roads and wild bears, they have arrived home safely.

The trip covered the southern tip of South America to northern Alaska, south-east across Canada and the US, and from Manchester to southern Spain.

A plan to traverse Africa from north to south was thwarted by the Arab Spring, so they flew to Johannesburg in South Africa, from where they explored southern Africa.

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Ms Hardy-Rix loved Alaska. ''It was so rugged, and so extreme. It was cold and grey on some days; other days sparkling blue, and grizzly bears would be walking along the side of the road''. Mr Rix said southern Chile was ''very much like Switzerland: big lakes, big mountains, with snow-capped chalets and glaciers''.

The toughest road was southwards down Ruta 40 in western Argentina - 3000 kilometres of dirt, with Antarctic winds.

They tried not to ride at night, but heading towards Popoyan, in Colombia, it was dark, rainy and foggy. They came around the corner on a mountain road into the path of two trucks, side by side. Mr Rix pulled the bike into a ditch and a truck missed them by 15 centimetres.

Ms Hardy-Rix found the slums in Peru confronting, but marvelled that people living in tin shacks would be cheerful, dress immaculately and work hard selling sunglasses at intersections.

In South Africa, a trip to a Zulu compound was curtailed because the warriors were striking over pay.

Mr Rix, a former president of the Police Association, was shocked to see South African farm labourers demanding a pay rise from 65 rand ($A7) to a paltry 150 rand a day, given fuel and food prices are similar to Australia's. He saw how such inequality could spur growing unrest in the country.

Asked why they did the trip, they said after the deaths of friends and relatives they didn't want to live with regrets.

Did they have any arguments? Ms Hardy-Rix said, ''the first time we did our big motorcycle trip [London to Melbourne 10 years ago] we argued about my lack of navigational skills. This time we had a GPS''.